The present invention relates to devices for measuring the gradient vector of a magnetic field. It relates more particularly to a measurement head for measuring the magnetic field gradient vector between two points in space as well as a magnetic gradient field vector measurement apparatus using such a head.
The value of a magnetic field can be accurately measured at a given point. This requirement of accuracy leads to designing apparatus whose sensitivity is such that their measurement may be affected by fluctuations of the ambient magnetic field. Thus, for example, small magnetic fields of the order of a nano Tesla can be measured with some magnetometers, whereas it is usual for the ambient magnetic field to present amplitudes with variations reaching a few tens to a few hundred nano Teslas in a frequency spectrum extending from the continuous to a few tens of Hertz.
To obtain accurate magnetic field measurements and to be able to correct them depending on the variations of the ambient magnetic field; it is possible to make different measurements at several points in the measurement zone with a non directional magnetometer. Thus a map of the magnetic field is established. This method has the drawback of being time-consuming.
Directional magnetometers may also be used, such as the magnetometers described in French patent application No. 79 30721 as well as in the first addition to this patent published under the No. 2 517 831. In this case, two magnetometers could effect the gradient measurement providing that their measurement axes are perfectly aligned. But such alignment raises problems. These problems are all the more difficult to solve the smaller the fields to be measured.
Thus, with the invention, these problems concerning the alignment of the measurement axes of these measurement devices may be solved.